Cushing syndrome, a fatal disease, is suspected in many thousands of patients each year, but confirmed in only a fraction of these. This project seeks to identify accurately which patients have Cushing syndrome, to define the etiology of their disease and to treat it optimally. We evaluated the utility of salivary cortisol as a screening test for Cushing's syndrome. Measurement of salivary cortisol would theoretically be a useful non-invasive test. We evaluated 136 inpatients and 4 outpatients with possible Cushing's syndrome, 16 inpatients and 7 outpatients with other non-adrenal disorders, and 34 healthy outpatients. Using cutpoints that excluded all subjects without Cushing's syndrome, we compared the sensitivity for the detection of Cushing's syndrome of nighttime salivary cortisol levels (2330 and 0000 h for inpatients and bedtime for outpatients), simultaneous inpatient serum cortisol levels, and urine glucocorticoid excretion. An assay-specific inpatient midnight or an outpatient bedtime salivary cortisol > 550 ng/dL (15.2 nmol/L) identified 93% of patients with Cushing's syndrome, and excluded all individuals without the disorder. Salivary cortisol measurements worked as well as plasma measurements, and better than urine glucocorticoid excretion. We conclude that bedtime salivary cortisol measurement is a practical and accurate screening test for the diagnosis of Cushing's syndrome. An additional initiative was to evaluate the utility of magnetic resonance imaging (MRI) for the identification of Cushing's disease. We hypothesized that the superior soft tissue contrast and thinner sections obtained with Spoiled Gradient Recalled Acquisition in the Steady State (SPGR) would improve tumor detection compared to the standard T1-weighted spin echo (SE) technique. We compared the performance of SE and SPGR MRI in 50 patients with surgically confirmed Cushing's disease. Compared to SE for the detection of tumor, SPGR had superior sensitivity (80% vs. 49%) but a higher false positive rate (2 vs. 4%). Based on these data, we recommend the addition of SPGR to SE sequences to improve the MRI detection of ACTH-secreting pituitary tumors.